Remove some stale stuff from clang target handling that came when I cloned the original target.
Make some changes to float handling.  Now, there isn't a separate floating point register class.  Instead, I just treat everything as the same IntReg class (which probably needs to be renamed) and make all patterns match bitcast eg. (fadd (f32 IntRegs:$a), (f32 IntRegs:$b)).  The compiler no longer fails with a mismatch, although it is now emitting calls to soft float intrinsics for some reason.